Block copolymers are known in the art for a variety of applications including the fabrication of impact resistant packaging materials, fabrication of molded articles and formulation of adhesives. Patent and scientific literature discloses numerous molecular variations of block copolymers which are suitable for such applications. See, for example, U.S. Pat. Nos. 3,639,517 (Kitchen); 4,221,884 (Bi) and Japanese Patent 52[1977]-129795. References which disclose the use of block copolymers to formulate adhesives include, for example, U.S. Pat. Nos. 4,780,367 (Lau), 4,444,953 (St. Clair); 4,556,464 (St. Clair); 3,239,478 (Harlan) and 3,932,328 (Korpman).
Not all block copolymers, however, are suitable for every adhesive application. For example, conventional star block copolymers are generally not suitable for use in removable tape applications wherein the tape is typically removed when it is no longer needed. Such applications require an adhesive that possesses a fourfold balance of tack, cohesive strength, adhesion and resistance to low stress peel. Especially important is the balance between the properties of adhesion and resistance to low stress peel.
When conventional monovinyl aromatic/conjugated diene star block copolymers (such as styrene-isoprene-styrene (SIS) star block copolymers) are used to formulate a tape having adhesion in the range desirable for removable tapes, the tape lacks sufficient resistance to low stress peel. When formulated to have sufficient resistance to low stress peel, the adhesion of the tape is often too high and the tape is difficult to remove. Often the peel and unwind are not smooth as well.
It is the object of the present invention to provide a novel block copolymer which can be formulated into a pressure sensitive adhesive. The pressure sensitive adhesive may be used to make a variety of different types of tapes including removeable tapes. Specific examples of the various tapes which may be made include masking tapes, packaging tapes, medical tapes and autoclave indicator tapes. Additionally, the pressure sensitive adhesive may be used to make protective sheeting, labels, and facestock.